This invention relates to computer controlled apparatus and, in particular, to sensing the presence of one or more modules in a modularly constructed apparatus.
The proliferation of computer control has lead to relatively fixed systems in order to simplify the control. In many applications, however, it is preferred to provide a control unit and one or more modules which can be selected at the option of the user. A problem arises in that the controller must "know" what components are attached to it. The brute force solution is to provide a different controller for each number and combination of modules. This is obviously inefficient to build and expensive to maintain.
The alternative to date has been to provide a local network over which the modules and the controller communicate. Such a system can be provided in one of several ways. A first is to provide a digital input for each module. Another is to multiplex signals to and from the various modules. A third is to send signals around a loop comprising the controller and the modules.
None of the alternatives is particularly easy to implement or inexpensive. Further, depending upon the equipment being controlled, timing may become critical. That is, these alternatives all require a finite service time for the controller. The time spent deciding which and how many modules are connected to the controller reduces the time the controller actually has to run the equipment.
A preferred embodiment of the present invention is described herein in the context of plasma reactors for use in the manufacture of semiconductor devices. It is understood that this is not the only use which can be made of the present invention.
Processing semiconductor wafers using a plasma involves somewhat of a dilmemma. Throughput is enhanced by batch processing the wafers. Control is improved by processing only one wafer at a time. One solution is to provide a plurality of processing stations, each taking a single wafer but working in parallel to increase throughput. However, some customers may not have the need or desire for parallel reactors while others may want to run several in parallel. Again, one can either build custom equipment for each market or adopt a modular approach wherein modules are cascaded to obtain the desired configuration. Further, modules can be mixed to obtain a closed system performing several distinct steps, e.g. etching, depositing, and stripping.
There is thus the problem of finding a way for the control unit to rapidly determine how many and what kind of modules are connected to it.
In view of the foregoing, it is therefore an object of the present invention to provide improved means for sensing the presence of a peripheral device by a computer.
Another object of the present invention is to provide means for sensing and identifying a peripheral device connected to a computer.
A further object of the present invention is to enable a computer to quickly sense and identify attached peripheral devices.
Another object of the present invention is to provide a field reconfigurable system which does not require reprogramming of a control unit.
A further object of the present invention is to provide a modularly constructed system which does not require different controllers for different arrangements of modules.
The foregoing objects and other advantages are obtained in accordance with the present invention wherein an analogue encoder comprises one input for each module. An analog to digital (A/D) converter is used by the computer to construct a digital signal representative of the attached modules. The analogue encoder comprises a binary weighted ladder resistance network. Modules are connected to the ladder, causing a unique signal to be generated for each combination of modules.
A more complete understanding of the present invention can be obtained by considering the following detailed description in conjunction with the accompanying drawings, in which: